The overall objective of this proposal is to determine the mechanism by which inoculation of newly hatched chicks with a non- pathogenic herpesvirus from turkeys (HVT) prevents the development of Marek's disease virus (MDV) induced lymphomas. Many of the studies will involve the use of a MDV induced transplantable lymphoma which has been developed and grows readily in an inbred syngeneic line of fowl. Efforts will be made to establish an in vitro passaged cell line to be used in studying surface antigens and cell-virus relationships in malignantly transformed lymphocytes. By the use of specific antisera, the T-cell and/or B cell component of the MD lymphoma, during various stages after implantation in birds of different histocompatibility genotypes, will be analysed. Reconstitution experiments with thymectomized and bursectomized recipients combined with the effects of HVT vaccination on growth of the transplantable MD lymphoma will be carried out to aid in elucidating the mode by which a non-oncogeic virus prevents tumor development.